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Feb. 14, 1956 w. R. HARRY 2,735,009

MULTIVIBRATOR CIRCUIT Original Filed Dec. 27, 1945 70 8 WWV ms 63 a0 6/62 as? $5 67% $5 65 FIG. 2

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K" cu TOFF VOLTAGE FOR DEV/CE 60 I VOLTAGE INVENTOR By M. R. HARRY ATTORAIFY MULTIVIBRATOR. CIRCUIT Wllliam-R..Harry,. Milwaukee, Wis.,assignor toBelliTelephone Lahoratories, Incorporated, New York, N. Y., acorporation ofi New: York Original application December 27', 1945,Serial No. 637,411. Dividedand tliis'application May 17,1950, Serial No.162,464

2 Claims. (Cl. 250-36) This is a division ofan application: of thepresent inventor, Serial, No. 637,411, filed December 27, 1 945, forSignal Translating Systems.

The present invention, disclosed in; the referenced; application,relates to oscillation circuits, and more specifically to such circuitsof the so-calledmultivibrator type.

The present invention is disclosed with particular reference to amultivibrator circuit, but it; will be evident that the features thereofmay find ready application to other types of circuits.

A feature of the invention comprises regulating the duration of a pulsegenerated by a multivibrator by abrupt, periodic or intermittent changein the time constant of a timing circuit of the multivibrator.

Another feature resides in efiecting such time constant changeresponsive to a conduction condition of one of two electronic devicesincluded in the multivibrator.

Still another feature involves constituting the timing circuit of animpedance network, in a specific instance, a resistor-capacitor network,and effecting the desired time constant change by introducing anadditional impedance in the network, in the specific instance, anadditional resistor.

Yet another feature comprises including electrical relay means in themultivibrator circuit for effecting the connection and disconnection ofthe means for changing the time constant of the timing circuit.

A further feature comprises establishing pulse generation by amultivibrator circuit at a preassigned recurrence rate, and periodicallychanging the constants of a timing circuit to establish a preassignedpulse duration.

Other features of the invention will be evident from the general anddetailed descriptions which follow.

In accordance with the invention, a multivibrator circuit embodying thefeatures of the invention may comprise a pair of electronic devices, inthe disclosed embodiment, electron discharge devices each comprising anevacuated envelope containing an electron source or cathode, an electrontarget or anode, and a control electrode or grid member interposed inthe electron path between cathode and anode for controlling orregulating electron flow therebetween. A timing circuit, comprising animpedance network and, in the disclosed embodiment, consisting of aresistance-capacitance combination, is interconnected between thecontrol electrode of one device and the anode of the other device; and asecond timing circuit, comprising an impedance network and which alsomay be a resistance-capacitance network, is interconnected between thecontrol electrode of the such other device and the anode of the onedevice. The cathodes may be connected to a point of reference potential;and the anodes connected to a source of potential positive with respectto that of such point. An electrical relay means is connected in one ofthe anode connections; and is responsive to conduction conditions ofsuch anodes device to connect and disconnect an impedance, specifically,a resistance, with respect to one impedance network to alter the timeconstant of the latter to a pre- 2,735,009 Patented; Feb. 14', 1 9561assigned degree, whereby the duration of the pulse gen: erated by themultivibrator circuit is determined.

A more complete understanding of the invention, and of its features andadvantages, will be obtained from the detailed description that follows,taken in conjunction with the showing, of the appended drawing, wherein:

Fig. 1 illustrates an. embodiment of the invention; and,'

Fig. 2 graphically illustrates operating features of; the circuit ofFig. 1'.

The oscillation or multivibrator circuit of the invention may beutilized, for example, to control an oscillator which may be anelectronic oscillation generator of' the class C type which is biasedso, that normally it is disabled'. The multivibrator circuit and theoscillator, the latter designated 11', are illustrated in Fig. 1, themultivibrator comprising a pair of electron discharge devices 6i) and.61, the anode circuit of the device 61 including a relay 62 havingarmatures 63 and 65 and associated contacts. The control grid of eachdevice is coupled] to the anode of the other by a resistance-capacitycombination, one coupling including the condenser 66 and resistance 67and, the other including thecondenser 68 and resistance 69 and, when therelay 62. operates, the res ance 70. The parameters of he. first. comb ao i. e., that defined by the condenser 66' and resistance 67, arecorrelated in ways Well known in the art, to determine the recurrencerate of the pulses produced by the multivibrator; the pulse length isdetermined primarily by the second coupling noted and is substantiallyindependent of the relay operate time as will be understood from thefollowing considerations.

In a conventional multivibrator of the configuration illustrated in Fig.l, but not including the relay 62 or resistance 74 the duration of theperiod in which the device 61 is conductive would be fixed by the timeconstant of the resistance-condenser combination 69, 68. That is, asillustrated in Fig. 2, if T2 is the time at which the device 61 isrendered conducting, the voltage upon the control grid of the device 60would vary as indicated by curve A, at a rate determined by theconstants of condenser 68 and resistance 69, and the device 61 wouldremain conducting until a time T3 at which this voltage reached thecut-off value for the device 60.

However, in a multivibrator of the construction illustrated in Fig. 1,when the relay 62 operates, at a time To indicated in Pig. 2, the timeTo-T2 being the operate time or" the relay, the resistance 70 isconnected in parallel with the resistance 69. Consequently, the voltageupon the grid of device 60 varies as indicated by the curve B and thedevice 61 is rendered non-conducting at time T1. The time T1T0 can befixed accurately, of course, by proper correlation of the constants ofthe condenser 68 and of the resistances 69 and 70. The release time ofthe relay is made small in comparison to the time T1T0. The circuitconfiguration is conducive to realization of small relay release timeinasmuch as the relay inductance is insufficient to prolong conductionin device 61 after device 60 becomes conductive. Thus, the period duringwhich the armature 65 is in engagement with its contact, whereby akeying voltage is applied to the oscillator device 11 to render itoperable, is T1To plus the release time of the relay 62.

Advantageously, in any particular multivibrator of the constructionillustrated in Fig. l, certain relations of the times should beobserved. Specifically, the time constant for the curve A should be madesuch, by correlation of the condenser 68 and resistance 69, that thetime T3T2 is long compared to T1T0. The relay release time should besmall as noted heretofore. In a typical system for producing3-millisecond pulses, i. e., for enabling the oscillator 11 for 3milliseconds, a relay having an operate time of 10 milliseconds and arelease time of ,illustrated and described, it will be understood thatmodifications may be made therein without departure from the scope andsubstance embraced by the invention.

What is claimed is: 1. A multivibrator circuit comprising a pair ofelectron discharge devices, each of said devices including a cathode, ananode and a control electrode, said cathodes being connected to a pointof reference potential, said anodes being connected to a point ofpotential positive with respect to that of said point of referencepotential, a timing circuit of preassigned time constant interconnectingthe anode of one of said devices and the control electrode of the otherof said devices, a timing circuit of preassigned time constantinterconnecting the anode of said other device and the control electrodeof said one device, and means for altering to a preassigned extent thetime constant of one of said timing circuits, said timing circuits eachincluding an impedance network, said means comprising electrical relaymeans connected in the connection of one of said anodes to said point ofpositive potential, and an impedance for connection with anddisconnection from the impedance network of said one of said timingcircuits responsive to the electrical condition of said relay means.

2. A multivibrator comprising a first and a second electron dischargedevice each having a cathode, control electrode and anode, acathode-anode circuit and a cathode-control electrode circuit for eachdevice, a first resistance-condenser timing means coupling the anode ofsaid first device to the control electrode of said second device fordetermining the recurrence rate of the pulses generated by themultivibrator, a circuit including a second resistance-condenser timingmeans coupling the anode of said second device to the control electrodeof said first device and including a normally-open auxiliary resistancecircuit, and an electromechanical relay including an operating windingconnected in the cathode-anode circuit of said second device and a pairof normally-open contacts connected in said auxiliary circuit forclosing said normally-open circuit upon energization of said operatingwinding.

References Cited in the file of this patent UNITED STATES PATENTS2,154,492 Clough Apr. 18, 1939 2,356,071 MacDonald Aug. 15, 19442,373,145 Sensiper et al. Apr. 10, 1945 2,428,058 Wise Sept. 30, 19472,458,283 McCreary Jan. 4, 1949 2,493,058 Bliss Jan. 3, 1950 2,514,677Skellett July 11, 1950 2,522,541 Saxton Sept. 19, 1950 2,549,505 MohrApr. 17, 1951

